In an electric vehicle or a hybrid vehicle, direct current discharged from a battery is converted to alternating current with using an inverter so that an alternating current motor is energized and driven. The inverter includes a plurality of semiconductor modules. Each semiconductor module has a semiconductor device and a pair of electrode plates disposed on both sides of the device. When the semiconductor device is operated, the device generates heat. Therefore, the semiconductor module is required to be cooled with various cooling means so as to reduce the temperature of the device lower than the permissible temperature limit of the device.
In a semiconductor device disclosed in Japanese Unexamined Patent Application Publication No. 2001-308263 (i.e., U.S. Pat. No. 6,542,365), a pair of heat sinks are disposed on both sides of a semiconductor module so that the heat generated in a semiconductor device is radiated to the outside through air-cooling fin of the heat sink. This cooling means using the air-cooling fin for radiating heat to the outside air has a simple construction and is a convenient means. However, a cooling performance, i.e., a cooling efficiency of the cooling means is not sufficient.
In an inverter disclosed in Japanese Unexamined Patent Application Publication No. 2001-345589, a pair of cooling units is disposed on both sides of a semiconductor device. A coolant flows in each cooling unit so that the semiconductor device is cooled. Further, in a cooling unit for cooling electric equipment disclosed in Japanese Unexamined Patent Application Publication No. 2002-95267, a pair of cooling member is disposed on both sides of a semiconductor device. A coolant flows in each cooling member and the device is pressed with a pair of cooling member so that the semiconductor device is cooled.
In the cooling means above, the heat generated in the semiconductor device is absorbed (i.e., heat-exchanged) by the coolant flowing through the cooling unit or the cooling member. However, inner pressure in and/or around the semiconductor device is increased extremely, to a degree that the semiconductor device or the inverter structure may be broken. Specifically, if anomaly happens in the semiconductor device (e.g., an excess current flow in the device, the excess current larger than the permissible limit), extreme heat is generated in the device. Then, a resin mold disposed around the device melts and vaporizes, so that an inner pressure inside the device is increased extremely. Therefore, the increased inner pressure pushes electrode plates of the device outward, while the electrode plates are sealed with the resin mold. If the electrode plate is deformed largely, the cooling member or the cooling unit may be destroyed, and/or the coolant may leak to the outside. Further, the whole semiconductor module may be destroyed, scattering pieces of the resin mold around the module, which in turn damage other parts of the equipment.